sAÜ
Fen Bilimleri Enstitüsü Dergisi 5.Cilt, 1.Say1 (Mart 2001) 69- 72The Characterization of a Bauxite Waste From The Bayer Process
Nevin Yalçın, Vahdettin Sevinç
Abstract --- The Bayer process for the alumina from bauxite produce a high quantity of waste in the form of mud. This waste -red mud- ııresent serious problems on environmental pollution. A possible solution for these wastes would be the utilization at the ceramic industry. Because of this, the characterization of a bauxite 'vaste has been performed using various techniques. The particle size distribution licd bet1veen 1 and 30 J.lm. The mean deıısit�i was 2.85 g.cm-3• The total weight loss \Vas fon nd as 7,07 o/o at 900°C from TG and DTG curves.
The results of XRD investigations showed that the red mud consist of hematite and sodium aluminium silicate hydratc crystalline phases.
Index Terms --- Bauxite waste, ı·cd mud, mineralo
gi
canaJysis •
I. INTRODUCTION
Bauxite waste-rcd nıud- is a by-product of the Bayer
process which is u sed for the production of alumina fronı
bauxite, and is generally discarded as a \tVaste
[ 1].
Thepartjclc size distribution lies betvveen
1
aııd30
�tm. 70o/c) of the parti cl es are fıııer than
5
�tnı. The amorphous contentis
very lıigh. There are rod-like crystals coated witl1 arnorphous n1aterial. Spheroidol particles are also con1n1on features of the microstnıcture and the larger pan ofthem are found in agglonıerates foım[2].
The redmu d
clıenücally con1prises of a ınixture of the fallawing oxides:Fe203� Ah03:- Si02,
Ti02, Na20
,KıO, M
gO
which con1prise the constituents of hematite, sodiun1 aluıniniuın si 1icate hydrate� sodalite, rutile, ete. mineral phases f3,4 J.
Red nıud present serious problen1s froın the vievv
point
of stor
i
ngon
environn1ental pollution. There fore� there is a need for an econonıical ınethods to solve orminirnise
the side effects of these problems. Severalstudies have been suggested that it has potential use in the following
fie1ds�
building blocks� floor and wall tiles?sanitary ware, adsorbent, flocculant, catalyzer, filler,
abrasivc, pignıent and cenıent ınaterial, the production of
pig
iron and alunüna.
A thorough evaluation of red muds N.Yalçın , V.Sevin� : Sakarya University, Arts and Sciences Faculty, Chemistry Departınent; Serdivan - Sakarya, 54180,TURKEY
can be accon1plislıed by a perspective of recovering all values contained in red n1ud with in the limits of process econonıy. Studies in this area is currently undenvay in the world
[5-12].
The accumulated anıoun1 i s ııearly •
3
ınHlions tonııes inSeydişehir-Turkey and there is not yet an cconomic vvay
or an application of plant scale to utilize the red nıud .. Although some work has been done on using red mud for construction material in Turkey. a detailed • • characterization of red mud was not presented [8]. The
aiın of this work is to characterize and study the physical, chemicaL nıineralogicaJ properties of
the
red mud.II. EXPERIMENT AL PROCEllURE
Tlıe bauxite �vaste-red ınud- vvas obtained froın Seydişehir Alunıiniunı Plant (Konya� Turkey. producing
200.000
tons of alıınıina per year) [13]. The \vaste 'vas homogenized through agitation, being detennind its density, huınıdity content and sıze of particle Aftenvards, the n1ud "vas dried at105°C for
3 hours and was screned to 7 5 J..Lffi in grain size. The obtained sample was subnıitted to clıen1ical and nıineralogic analysis�deternıinatioıı of density, theıınal analysis, structural
observation.
The red ınud sample \Vas fused vvitlı Na2C
0
3- K2C01
in the
1100° C
at the p lutinunı crucible and vvas dissolved vvithHCl.
Chcınical analysis vvas perforn1ed using an ato1nic absorption spectrophotoıneler (Rank Hilger, Aton1 Spek
H-1580),
a digital photoıneter (Dr. Lange LP 2W) and we1. chemical ınethods.The specific surface area
of
red ınud \Vas ıneasured using the Brunauer, En1111ett and Teller (BET) nıethod witb an adsorpmeter (Model Flow Sorb11-2300
Micromeritics)
Deıısity measurement �vas done by a picnometer and particle size measurement performed by a sedigraph
(5000
D Micronıcritics). For the particle size nıeasurenıeııt, the sanıples vvere dispersed ultrasoııically in a0,5
<x) solution ofNa4P207,10
HıO.The Characterization of a Bauxite Waste From The Bayer Process
Thermal analysis was carried out • by • a simultaneous thermal analysis instrument (Netzsch-429). 100 nıg of
sample were placed in a platinum cup for the analysis. The curves were recorded under air atmosphere. The heating rate was 1 0°C/min. The interval of study was
20-ı2000 C.
X-ray diffractometry
(XRD)
diagram of the sample was obtained with a diffractometer (Philips PM 990 ı; 00).The infrared spectruın (IR) of the san1ple in a K.Br matrix vvas carried out with a FTIR spectron1eter (Mattson FTIR Spectronıeter).
lll. RESUL TS AND D ISCUSSION
The honıogenized red n1ud sanıple of the original bauxite has a hunıidity content between 40 and 50o/o and a mean density of 2.85 g.cm-3. The specifıc surface area value of the red nıud is 20.9 m2.g-1.
Granulometric analysis
Tlıe particle size
analysis
of thered mud is
givenin
Figure ı. The data on particle size analysis has indicated •
that the mean size of particle is relatively fine. . '
88 %
of the particles are finer than ı O �tm.'N�ıght (%J ıoo r-- 1-� 1-� 1"' V so 1-� r'
1-fo-�
� r-' to-1- �o-... � ı-i-.. ı ... o 1 ı ' r ı T T ı )0 100 Particle size (�lm)Figure 1. Particle size analysis of Seydişehir (Turkey) red mud
Chemical Composition
The chemi�al analysis of the red mud is given in Tab le
�·
The ch��1ıcal analysis of batL-xite waste was pelformed ın the orıgınal sanıple. For the average value was nlade fıve tests.The percentages of Fe20 Al 3, 2 3,O
sı·o 2 an dNa20 are nıore than others.
70
Table 1. Chemical analysis of Turkishred mud
Compounds Content
(Wt %)
Feı03 35,73 Alı03 23,29 Si02 ı2,08 Ti02 5,08 Na ıO
ı0,26 KıO
0,28 CaO
2,81 MgO
1· 0.76 co2 2,40 so3 ı,34 Loss on ignition 8,45 (1000°C) Therınal analysisThe theı ı na 1 analysis of the red mu d is shovvn in Figure
2. The TG/DTG curves for the bauxite \Vaste sample were recorded after desiccation at 1 0
5
°C 1 3h. Fromthese cuıves of the red nıud . the total vveight loss was
found to be 7. 07o/o at 900°C. As can be observed in the
TG and DTG curves� in the 25-900°C range, there is a
continuous loss of vveight due to the volatilization of
\Vatec so3 aııd C02. The formation peaks of free water.
\Vatcr Of CI)'StallizatİOll, SÜ3 and CQ� observed at abOU'
290°C, 530°C,750°C and 890°C respectively.The peaktc 7 soo c corresponds to the decoınposition of iron sulphate
probably
[
ı4]
. But this ınineral w as not searched at theXRD analysis. Carbonate decomposition \vith C02 was
evoluated below 900°C
(15,16].
Weight (o/ö) TO ı TG2 DTG 100 200 300 400 500 600 700 800 900 1000 ll 00 1200 Temperature ec)Figure 2. Thermal analysis curves of red mud
'J.Yalç1n, V.Sevinç
Mineralogy
Table 2 shows the results obtained froın the X-ray
diffraction diagram of the red mud. The presence of
hematite ( a- F e203) and sodium aluminiunı silicate
hydrate (1.01 Na20. Ah03. 1.68 Si0ı.l.73 HıO) has been •
identified.
Besides these phases, sodalite (Na4Al3Si3Üıı (OH)), sodium silicate (NaıSi03), sodium aluminiunı oxide
(NaA102), iron titaniuın oxide (Fe2 Tiüs) calcium silicate (CaSi03), sodium titanium oxide (Na2 Ti30;), sodium carboııate (Na2C03) phases were detected.
Table 2. XRD analysis of red mud
Mineral names Fornıula
Hematite oc- Feı03
Sodiun1 aluıniniuın 1�01 Na20. Alı03.
Silicate hydrate 1,68 Si02. 1, 73 H20
Sodalite Na4 Al3 Si3 Oıı (OH)
Sodium silicate NaıSi03
Sodiun1 aluntiniuın oxide NaAI02
I ro n titanium oxide Fe2TiOs
Calciuın silicate CaSi03
Sodiun1 titanium oxide Na2Ti307
Sodiunı carbonate Na2C03
Infrared Spectroscopy
Figure 3 slıovvs the infrared spectrum
(IR)
of a sample of bauxitc waste in a KBr ınatrix.···---·-··· · ···-
�
ı (\l:
� 1 ' • '' �s.i 1 \ � i r .f
� .. __,�/··-\
f
�
1\
i
, ; ---- ;. ,;� ,} \ ! � .. 1·1\ :·v·
: t' � \� vt: \ : � �� ı ·' • /\ � ... � <.: \ 1 . � ·ı �!) . : /�·
,, �:.: \ �"! � .// � ... l �� .�.!
/./
�
- �·ı
i
·� � : �/�
.
'/·o."...
� � . ı : t <�� '.. / ri � ::�
ı
\�
.··· .\
1:
� j ı ! �«J'j
�·H
y
,___ ______ __ ·-···· ···-···�---�-� . .... ............. . 3500 30CC 7.�00Figurc 3. lnirared spectrum of red mud
t!XJO 1 sc.-v ıooo �
In the 2000-4000 cm-1 region a wide absorption appears w hi ch can be assigned to the stretching modes of \Vater molecules absorbed on the bauxite waste surface or to enve1ope of H-bonded surface OH groups. The
band at 1647 cm -ı is due to the H20 bending mode.
2360-2342 cnı-1 bands are due to from the background of
the instnın1ent also. The bands at 1475 cm -J and 141 0
cnı 1 show· the organic matter in red mud. The 1000 cm-1
band is the strong Si-O band .. which can be assigned in the 900-1200 cm-1 region. The 688 cnf1 band show the
sulphates. 660, 560 ,474 cnı"1 bands are attributed to
henıatite [ 14] .
CONCLUSIONS
The original bauxite-red ıııud sanıple has a humidity
content between 40 and 50
%
and a mean density of2.85 g.cnf3, 88 %of the sample having a snıaller size
than 1 O f.!ID. The results of chemical and ıninera1ogic
analyses have demonstrated that Feı03, Al203, SiOı, Ti02, CaO and Na20 represent the oxide nıajority conıponents and heınatite.. sodiuın aluınini un1 silicate hydrate the principal prcsent crystalline phases. Concerning the TG/DTG curves, the forn1ation peaks of
free water, water of crystallization, so3 and co2
observed at about 290°C. 530°C, 750°C and 890°C respectively. The infrared spectrun1 sh o wed the characteristic bands of the n1atters in the red ınud.
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